Environmental health risk assessment of particulate air pollution and mortality in metropolitan Manila, Philippines
Key Words: Metropolitan Manila, Environmental Health Risk Assessment, Life Expectancy, Age, Educational Level, Particulate Air Pollution, PM10 Background and Objectives: Metropolitan Manila is considered a Mega-City with approximately 10 million people as of 1995. Due to rapid industrialization and urbanization, environmental health problems including air pollution have become very prominent. In this study, the potential magnitude of environmental health inequalities with particular reference to particulate air pollution in Metropolitan Manila, Philippines has been assessed in terms of mortality by adapting the risk assessment method. Utilizing various indicators of mortality such as life expectancy and years of life lost, modification of the chronic health impact by markers of population heterogeneity particularly age and educational attainment has been explored In addition, the impact of various pollution reduction scenarios were evaluated. Methodology: Published Environmental Health Risk Assessment methods were adapted and applied for estimating chronic mortality effects of PM10 pollution in the city of Metropolitan Manila. Pooled estimates derived from the exposure-response coefficients of the two US longitudinal epidemiological studies on PM10 and chronic mortality were used primarily. These pooled estimates which signify increases in mortality with incremental increase in PM10 were applied to the indicators of mortality. Hence, the methodology involved a life table approach using age-specific mortality rates from Metropolitan Manila in 1995. Annual averages of PM10 for the whole of Metropolitan Manila and for the cities within were also used. Life expectancies using two pollution reduction scenarios were compared with the 1995 life table to determine pollution reduction benefits. All causes and cardio-respiratory causes of deaths were evaluated. Apart from gains in life expectancy, other effect measures such as years of life loss and number of deaths were also assessed. Findings: Health impact as a result of particulate pollution reduction by 10 μg/m3 resulted in gains in life expectancies of approximately five months for both males and females. Inclusion of effects on the elderly in the model did not make much of a difference in terms of life expectancy gains. However, with the addition of the effects on infants in the model and retaining the effects on adults and the elderly, life expectancy gains, years of life lost and attributable deaths increased. Life expectancy gains were also estimated to be more for the low education level as compared to the middle and high education levels. The overall life expectancy gains for a reduction to the international annual guideline of 50 μg/m3 PM10 scenario were 2.22 years for males and 1.88 years for females. By educational level, the life expectancy gains at age 25 years old in the same pollution reduction scenario, range from 0.74 years for males and 0.59 years for females in the high educational level to more than four years for males and more than three and half years for females in the low educational level. Improvements in the cardio-respiratory causes of death alone contributed most to the life expectancy gains. The estimates that resulted from this assessment were found to be sensitive to the exposure-response coefficients used, the exposure reduction scenarios, the measures of heterogeneity (particularly age and educational level), baseline rates and the time period of effect. In addition, geographic differences in gains in life expectancy within Metropolitan Manila were like wise assessed. Higher gains in life expectancy were seen in the cities in the north where pollution levels are also greater than in the cities in the south. Implication: The air pollution studies have found relatively small exposure response coefficients. However, the impact on public health is quite substantial and relevant to prioritising intervention to control air pollution. The results in this study could be used in several aspects of public policy as discussed in the thesis. These results were presented to decision-makers in the government and the responses summarised.